1. Field of the Invention
This invention relates in general to water treatment and, in particular, to ballast water treatment for ships. More specifically, but without restriction to the particular embodiments hereinafter described in accordance with the best mode of practice, this invention relates to in-port water treatment systems directed to filtering ballast water and deactivating biological material to prevent translocation of aquatic invasive species.
2. General Discussion and Related Art
Over the past 25 years, the introduction of foreign aquatic invasive species (AIS) into ports and waterways has increased significantly throughout the globe. Ships from around the world pump 40,000 gallons of foreign ballast water into U.S. waterways every minute.
This discharged ballast water contains countless species of foreign marine life including fish, shellfish, plants, and microorganisms. More than 200 AIS are now established in the San Francisco Bay and Delta areas in California and 150 AIS in the Great Lakes of North America alone.
Many of these foreign AIS are disrupting the local marine ecosystems. Invading organisms are steadily replacing native species by competition or predation. Viruses and bacteria carried in ships ballast water have the potential to cause the destruction of native species as well as create human health problems.
The Zebra Mussel, Chinese Mitten Crab, Sea Lamprey, and Purple Loosestrife are just some of the AIS causing serious and costly problems globally by clogging canals and water intake and/or outlet systems. Billions of dollars have been spent on problems arising from these organisms. The primary source comes from the discharge of ships' ballast water, taken in as ballast in one port then discharged into another port.
Globally, there are seven major marine ecological zones, each having distinct marine species which have evolved in those zones over many millennia. In recent years, however, there has been significant displacement of indigenous species from one zone to other zones around the globe. Today, no country has escaped from the widespread impact of aquatic invasive species arriving from other marine environments. In many instances, these translocated species have prospered in their newly found environment with damaging economic and ecological consequences. According to recent studies conducted by marine scientists, the most significant contributing factor for these undesired re-locations is the discharge of ballast water contained in vessels of commerce. Typically, an ocean going vessel takes sea water into its ballast tanks prior to departing its port of origin to stabilize the vessel during its voyage. This ballast water from the home port may then be discharged at ports of call in other ecological locations. Currently at least 162 non-indigenous aquatic species have colonized the Great Lakes alone. Thus far, the economically most significant aquatic invader to arrive in the Great Lakes system is the zebra mussel. A 1988 import from the Black Sea, the zebra mussel has become an economic and ecological disaster in this region. In addition to ecologically contaminating the Great Lakes, the zebra mussel is now spreading rapidly to other waters within the United States in spite of massive efforts and methodology deployed to control this invasive species. For all foreign aquatic species invading United States waters, the U.S. Coast Guard estimates the collective domestic economic impact of these undesired AIS arrivals at more than $7.3 billion per year.
The world's nations and different states of the United States are responding to this threat by promoting treaties and state legislation directed to setting standards for halting the spread of aquatic invasive species. On the international front, the International Maritime Organization (IMO) is developing an IMO Convention relating to ballast water management requirements. This Convention is expected to be signed within a few years then ratified by national legislative bodies and entered into force as domestic law in several of the world's nations. It is currently anticipated that after the year 2008, all international trading vessels using seawater as ships ballast will fall under the IMO Convention. Royal Haskoning Report, Global Market Analysis of Ballast Water Treatment Technology, Oct. 24, 2001, Reference No. 42810/001R/HSC/SKO.
On the U.S. domestic front, the states of Washington and California are leading state legislative development efforts directed to regulating the discharge of ballast water into their respective state ports. These regulations are technical in nature and will provide specific standards relative to the discharge of particulate matter and active biological organisms.
Prior to current state legislative activities and collective international concern, the shipping industry had shown an acceptable degree of compliance to pre-existing standards. However AIS are still being introduced into the world's ports and waterways. Thus prior standards and technical measures implemented over the past years have proven inadequate. Currently, no known economically viable system has been found to prevent these organisms from entering or leaving ships' ballast water tanks.
Some of the prior methods and devices that have been employed in an attempt to control the AIS problem include (1) the mid-ocean ballast water exchange method, (2) ozone and nitrogen systems, (3) cyclone systems, (4) heat systems, and (5) use of biocides. These prior methods and systems are briefly described in further detail immediately herein below.
Mid-ocean Ballast Water Exchange: The U.S. Congress has passed legislation requiring ships carrying ballast water from foreign ports to exchange this point-of-origin ballast water with mid-ocean sea water before entering the Great Lakes. This method has not proven effective in killing freshwater organisms. Very small quantities of survivors, one per several thousand, were found sufficient to start an invasion.
Ozone and Nitrogen Systems: These gases, when introduced to the ship's ballast water, were found to be effective in controlling bacteria and other small organisms. However, they have proven to be less effective at controlling adult crustaceans and fish. Other disadvantages of these systems include those next enumerated. (1) Problems of uniformity in mixing the gases with the ballast water. Several days are required to kill the organisms. Ballast water exchange sometimes takes place within several hours. (2) Unable to treat the organisms in the sediments which are disturbed during ballasting. (3) Requires modification to the ship and significant space on board for system installation. (4) High cost.
Cyclone Systems: Water drawn into the system for ballasting is spun to remove organisms. The filtered water is allowed to flow into the ballast tanks and the removed organisms and unfiltered water returned to its source. These types of systems are capable of removing sediments, large particles, and some organisms. The disadvantages of these systems include the following. (1) Centrifugation does not work effectively with organisms that have densities close to that of water. (2) The system is prone to clogging and must be back flushed to clean. (3) An inability to treat or remove organisms that passed through the system. Once in the ballast tanks, these organisms may continue to grow and multiply. (4) Requires modification to the ship and significant space on board for system installation. (5) High cost.
Heat Systems: Heat energy high enough to kill organisms is added to the ballast water. Disadvantages of these systems are next briefly listed. (1) Huge quantity of energy is required to raise the temperature high enough to kill organisms. The energy required to kill bacteria and viruses make this system impractical for ballast water treatment. (2) Problems of uniformity in mixing the heated water with the ballast water, requiring many hours to kill the organisms. Ballast water exchange may have to take place within several hours. (3) Enough energy to run the system may not be available from the ship's power system. (4) High cost to install and operate.
Use of Biocides: Biocides such as vitamin K and chlorine are effective at killing AIS when added to the ballast water. Disadvantages of these systems include the following. (1) Problems of uniformity in mixing the biocide with the ballast water, requiring many hours to kill the organisms. Ballast water exchange may have to take place within several hours. (2) Some bacteria and viruses may not be killed by the biocides used. (3) Treated ballast water may be toxic to the environment when discharged.
In addition to the above technical limitations and cost considerations, none of the known prior art ballast water treatment systems will meet the newly emerging regulatory standards. Therefore it is desired to provide a cost effective, technically efficient ballast water treatment system that is acceptable by the marine shipping industry and that satisfies the emerging more stringent regulatory standards.